Existing Blow Out Preventers (“BOP”) function on hydraulic systems. For those systems that use electricity, the electrical system is used to power an open loop with no feedback, low power, unidirectional actuator, such as a solenoid. This unidirectional actuator then controls a hydraulic pilot valve that passes a hydraulic power signal to a high power actuator, such as a SPM valve, which in turn passes hydraulic power at flow rates and pressures sufficient to operate a BOP ram or other BOP functions. The release of the electronic actuator, the pilot valve, and the main valve rely on a spring return and are also of open loop design.
Existing BOP systems use electrical power for light loads consisting of small power actuators (described above) and limited sensor and computational capability. This electrical power is delivered from the vessel via an umbilical cable, through a high voltage Alternative Current (AC). The high voltage needed to maintain peak current, however, leads to insulation stress and breakdown, allowing salt water ingress, galvanic corrosion of the cable, and possible hydrogen embrittlement of metal conductors. The high current requirement results in selection of heavy, non-flexible cable that is difficult to terminate and causes kinking issues. These cables are difficult to store onboard the vessel. Additionally, communications lines may be integrated in the umbilical and AC power creates magnetic field disturbances and line noise in the communications lines.
For deep water applications, deliverable current is limited, both by the extreme distances of transmission and by the risk of communication line interference. Because of the risk of losing the power link with the surface, existing BOP components are designed to operate under no-power conditions. For example, the unidirectional actuator that controls the hydraulic pilot valve incorporate the aforementioned spring return that allows the valve to turn off even when power is lost. However, engagement of the actuator requires sustained power from the surface, which limits the amount of actuators that can be engaged at any one time. Moreover, loss or disturbance of power from the surface results in loss of communications and further causes a change in position of all powered solenoid actuators. This may cause unwanted hydraulic changes to the BOP functions.
The few sensors used on existing BOP technology measure pressure, flow and other physical parameters in an attempt to provide feedback for components operating in an open loop by attempting to confirm that a particular function was actuated or completed. The use of central sensors forces only one function to be operated at a time because the feedback of central pressure and flow sensors would be unclear if multiple functions were operated simultaneously. The integrated nature of the system, where there is extensive shared infrastructure, forces the use of significant levels of single application software. This software, and the off-line support systems for it are written for a very limited number of applications. The result is poor predictability, difficulty in troubleshooting, and weak industry-wide support